Growth of a chrysoberyl single crystal displaying a luminous band effect has been attempted hitherto by making a raw material bar using beryllium oxide, aluminum oxide and titanium (III) oxide, by growing a single crystal with a condense-heating floating zone method, and by carrying out further heat-treatment.
However, because the production of the raw material and the growth of a crystal are carried out in a normal atmosphere, titanium becomes quadrivalent, making it difficult to solid-dissolve it into the chrysoberyl single crystal, and making it difficult to obtain a single crystal even if it does solid-dissolve to some extent. Accordingly, the production of a chrysoberyl single crystal in which titanium is solid-dissolved has been difficult, and the resultant single crystal does not display a luminous band effect even after heat-treatment.